Showing papers by "Thomas T. Veblen published in 1999"
TL;DR: The effects of humans and climatic variation on fire history in northern Patagonia, Argentina, were examined by dating fire scars on 458 trees at 21 sites in rain forests of Fitzroya cupressoides and xeric woodlands of Austrocedrus chilensis from 39° to 43° S latitude as discussed by the authors.
Abstract: The effects of humans and climatic variation on fire history in northern Patagonia, Argentina, were examined by dating fire scars on 458 trees at 21 sites in rain forests of Fitzroya cupressoides and xeric woodlands of Austrocedrus chilensis from 39° to 43° S latitude. Climatic variation associated with fires was analyzed on the basis of 20th-century observational records and tree ring proxy records of climatic variation since approximately AD 1500. In the Austrocedrus woodlands, fire frequency increases after about 1850, coincident with greater use of the area by Native American hunters. Increased burning, particularly in the zone of more mesic forests, is also strongly associated with forest clearing by European settlers from about 1880 to the early 1900s. The marked decline in fire frequency during the 20th century coincides with both the demise of Native American hunters in the 1890s and increasingly effective fire exclusion. Strong synchroneity in the years of widespread fire at sample sites disperse...
282 citations
TL;DR: In this paper, the authors quantify changes in fire frequency along a gradient from mesic Nothofagus dombeyi forest to xeric woodlands of Austrocedrus chilensis at the steppe ecotone.
Abstract: In northern Patagonia, Argentina we quantify changes in fire frequency along a gradient from mesic Nothofagus dombeyi forest to xeric woodlands of Austrocedrus chilensis at the steppe ecotone, and we examine patterns of vegetation change coincident with the changes in fire regimes across a range of spatial scales. At a regional scale changes in land cover types are documented by comparing 1:250 000 scale cover type maps from 1913 and 1985. Changes in landscape structure are analyzed by comparing vegetation patterns on 1:24 000 scale aerial photographs taken in 1940 and 1970. Fire frequency peaked in the late nineteenth-century due to widespread burning and clearing of forests by European settlers late in the century. Subsequently, fire frequency declined dramatically about 1910 due to the cessation of intentional fires and has remained low due to increasingly effective fire exclusion. At a regional scale there has been a dramatic increase during the twentieth century in the proportion of forest cover relative to areas mapped as recent burns or shrublands in 1913. Remnant forest patches that survived the widespread late-nineteenth century burning have coalesced to form more continuous forest covers, and formerly continuous areas of shrublands have become dissected by forest. Under reduced fire frequency there has been a shift in dominance from short-lived resprouting species (mostly shrubs) towards longer-lived species and obligate seed-dispersers such as Austrocedrus chilensis and Nothofagus dombeyi. Due to limited seed dispersal of these tree species, the spatial configuration of remnant forest patches plays a key role in subsequent changes in landscape pattern.
109 citations
TL;DR: In this article, the authors examined spatial patterns of tree age and size to determine if they are consistent with the episodic pattern of tree regeneration proposed for ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws).
Abstract: Patterns of stand development may be interpreted from spatial analyses, based on variables such as tree age and size, together with past records of climate and disturbance. In the present study, our objective is to examine spatial patterns of tree age and size to determine if they are consistent with the episodic pattern of tree regeneration proposed for ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) and expected changes in tree spatial patterns as cohort patches age. According to our hypothesis, internal patch structure should become less clumped as single cohort patches age due to self-thinning, with few trees attaining dominance in a small patch. In this study, tree spatial patterns in 16 stands of P. ponderosa in the Colorado Front Range are described and related to patterns of stand development. Analytical methods included Ripley's K(t) (a univariate statistic of tree spatial distribution), Ripley's Kt 12 () (a bivariate statistic of spatial association), and Moran's I (a measure of spatial autocorrelation). Spatial patterns imply establishment of patches of pines followed by self-thinning. Continued stand development results in strong size hierarchies as manifested by stronger spatial autocorrelation of tree age than tree size. Hence, pines exhibit a strong size class hierarchy developed within an even-aged patch. Resume : Le patron de developpement d'un peuplement peut etre interprete grâce a l'analyse spatiale, en se basant sur des variables telles que l'âge et la taille des arbres, ainsi que sur les donnees historiques du climat et des perturbations. Dans cette etude, notre objectif est d'examiner les patrons spatiaux d'âge et de taille des arbres afin de determiner s'ils concordent avec les patrons episodiques de regeneration des arbres proposes pour le pin ponderosa (Pinus ponderosa Dougl. ex P. & C. Laws.) et les changements attendus dans la distribution spatiale des arbres a mesure que les groupements de cohortes vieillissent. Selon notre hypothese, la structure interne des groupements devrait etre de moins en moins en grappes a mesure que les groupements de cohortes individuelles vieillissent suite a l'eclaircie naturelle, menant a la presence de peu d'arbres dominants dans les petits groupes. Dans cette etude, les patrons spatiaux de 16 peuplements de Pinus ponderosa situes dans la Colorado Front Range sont decrits et relies aux patrons de developpement des peuplements. Les methodes analytiques incluent le K(t) de Ripley (une statistique univariee de distribution spatiale des arbres), le Kt 12 () de Ripley (une statistique bivariee d'association spatiale) et le I de Moran (une mesure d'autocorrelation spatiale). Les patrons spatiaux laissent supposer l'etablissement de groupements de pins suivi d'une eclaircie naturelle. La poursuite du developpement des peuplements entraine une forte hierarchisation de la taille des arbres etant donne que l'autocorrelation spatiale de l'âge des arbres est superieure a celle de leur taille. Les pins demontrent donc une forte hierarchisation des classes de taille, qui se developpe a partir d'un groupement d'âge uniforme.
80 citations
TL;DR: In this article, old-methodological Sneakers: Fashion and Function in a Cross-Training Era are discussed. But the authors focus on the cross-training of the shoes.
Abstract: (1999). Old Methodological Sneakers: Fashion and Function in a Cross-Training Era. Annals of the Association of American Geographers: Vol. 89, No. 4, pp. 679-687.
27 citations
7 citations